We proposed to purify from human placenta the cytochrome P-450 enzyme which catalyzes the aromatization of androgens to estrogens. The enzyme will be characterized with respect to substate specificity and kinetics, physicochemical properties and partial amino acid sequence. We also proposed to prepare both polyclonal and monoclonal antibodies to the purified protein. In addition, we propose to investigate the interaction of several types of active site-directed inhibitors as probes of the structure and function of the enzyme. Two types of reversible inhibitors -- non-steroidal compounds which mimic the androgen substrates and a new type of bifunctional steroid inhibitor - will be used for mapping the active site geometry. Several types of chemically reactive steroids -- direct alkylators, suicide substrates and photo-affinity reagents - will be used to covalently label the protein in order to identify regions of the protein sequence which comprise the active site. The inhibitors will be of heuristic use for studying details of the molecular events of the aromatization reaction and will have an application in the design of drugs for the treatment of estrogen-dependent cancers.